Is there anybody out there?

With the discovery of an Earth-like planet near the centre of the Milky Way, Yorkshire scientists reveal why discovering the final frontier may not be light years away. Martin Hickes reports.

It was a case of two plus two equals five.

When scientists yesterday revealed they had discovered a planet similar to Earth, those who spend their lives convinced that ET was a factual documentary and who spend their spare time being abducted by aliens and then telling everyone else about it, nodded their heads, smugly convinced they had been right all along.

But as always, the devil is in the detail, and beneath the spin which screamed "breakthrough in the search for extra-terrestrial life", the actual truth was the planet, some 20,000 light years away from our own, was in fact too cold for any form of life to survive. But the conspiracy theorists may yet be proved right – they may not have found life this time, but they're definitely getting warmer.

It was some 25 years ago when American astronomer Carl Sagan – as well known in the US as Patrick Moore is in Britain – screened Cosmos, a ground-breaking series of programmes, which considered the likelihood of life existing on other worlds within our galaxy.

Sagan, who once famously said, "If you wished to bake an apple pie from scratch, then you must first invent the universe", ambiguously concluded that among the billions of unknown planets, the number which may contain life may be as small as 10 but as great as one million.

A generation down the line, and thanks to the recent discovery of at least 160 planets around stars other than ours, those figures from 25 years ago might well need to be revised.

Yorkshire scientists, in collaboration with many colleagues at seats of academic learning across the UK, are now at the forefront of the search for the tell-tale signs of new planets around distant stars.

Ren Oudmaijer, from Leeds University's School of Physics and Astronomy, has spent a lifetime studying the formation of stars and planets, and is optimistic that Earth-type planets may one day be discovered – and much sooner than many predict.

"We have made quantum leaps in the identification and study of the formation of planets since Carl's day," he says.

"Personally, I would think that our chances to discover life elsewhere within the universe by the end of the century have increased dramatically.

"While we currently cannot observe the planets directly, a host of new telescopes set to be launched within the next few years, operating from outside our atmosphere, will more readily be able to pinpoint the tell-tale wobble of the light from a star when the planetary candidate passes in front of it.

"In the last decade, astronomers have found that approximately 10 per cent of the star systems they examine have massive planets – worlds at least as large as Neptune, and often a few times the mass of Jupiter.

"It's not unreasonable to suggest that within the next generation, we will witness the discovery of Earth-type planets around other suns."

Astronomer Seth Shostak, from the world-famous SETI Institute in California confirms there is every reason to be optimistic about the number of planets – including those of Earth-size – which might exist in the galaxy. For him, Sagan's universe may not be just an apple pie, but a metaphorical three-course meal full of exotic delights, including dark matter

"Carl Sagan was not pessimistic per se about the number of civilisations which may exist through the galaxy," says Shostak. "Of course, we still don't know whether life exists elsewhere in the galaxy – that much hasn't changed in 25 years. What we do know is that many planets now exist around stars – some astronomers think perhaps 90 per cent of the stars we see have planets – and that we will soon be able to more readily identify Earth-sized planets – perhaps as soon as within 1,000 days from now, given the upcoming

launch of NASA's Kepler mission.

"A project planned for 2008 will allow our generation to be the very first to create an inventory of planets orbiting other suns, which is tremendously exciting.

"Many of them could be Earth-sized. Personally, I think the number may be as common as summer mosquitoes. That's not to say they will have life, of course, as that depends on a host of other factors, but if we have the inventory, we are one step closer to learning if they do.

"If Carl were around today, he would be tremendously excited by the prospect of such an inventory, an accomplishment which will be something unique in human history".

Yervant Terzian from Cornell, Sagan's former university, adds: "Certainly, Carl would have been excited with the discovery of planets around other nearby stars.

"He believed that most stars should have planets, and many should have conditions where complexities could

form.

"The big question now remaining is the longevity (of any intelligent civillisation capable of communicating with us). Many indications seem to say it is short, and that may be why we have not heard from anyone."

So, 25 years after Cosmos,

it may just be possible that the discoveries of the Kepler probe may just result in "billions and billions" of planets, to paraphrase Sagan's famous phrase.

THE NEW PLANET

Located near the centre of the Milky Way, about 20,000 light years from us, the latest new planet, discovered as a result of an international project involving 73 scientists from 12 different countries, is too cold for survival but scientists are now hopeful that other habitable ones may exist.

"Our next goal is to find more of them, with lower masses, in order to measure the abundance of cool Earths and determine if habitable planets like Earth are abundant or rare," says collaborator Professor Keith Horne from the University of St Andrews.

"If the abundance is high, the next step is to search for life on those planets."

The new planet, which has been given the title OGLE-2005-BLG-390Lb, has a mass five times that of Earth and orbits a parent star some five times smaller than the Sun.

It is likely to have a thin atmosphere like Earth, and its rocky surface is thought to be deeply buried beneath frozen oceans. "We have not yet found a true analogue of the Earth, but at least we know that small planets exist that are either hotter or cooler than the Earth," explained fellow collaborator Dr Martin Dominik, also from St Andrews University.

The planet was located using a technique known as gravitational micro-lensing, noted by Einstein as far back as 1912.

The method relies on light from a background star being bent by the gravitational field of a dimmer star in the foreground, acting as a lens.

Planets can then be viewed orbiting the lens star. This latest discovery is the third planet to be detected using the technique.

The nearest other Earth-like contender is GJ 876d, a planet 7.5 times the mass of Earth but which is too hot to support life.

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